Scientists capture immune cells attacking live melanoma cells in real time

Scientists at the Garvan Institute of Medical Research have captured, for the first time, 'housekeeping' immune cells actively attacking and engulfing live melanoma cells – a discovery that could change the way we approach treatment for one of Australia's most common and deadly cancers.

The findings, published today in the Journal of Experimental Medicine, reveal a previously overlooked population of immune cells called macrophages that patrol the edges of melanoma tumors, steadily engulfing cancer cells and slowing tumor growth.

Dr. Yuki Keith, first author of the researchThis is the first time anyone has captured a macrophage attacking and engulfing a live cancer cell in real time. We always suspected macrophages were doing more than we gave them credit for – now we have the video footage to prove it. Studying this in a living system is crucial because it is more representative of what happens in real life, showing the complexity of the immune system and paving the way for the treatments of the future."

A hidden army in the skin

In the past, researchers have tried indiscriminately eliminating all the macrophages in the body to see how it affects the tumor.

However, Dr Keith's team found that not all macrophages in the skin were the same, identifying one particular subpopulation that expressed a protein called CD169. By specifically targeting and depleting these CD169-positive macrophages, they found the tumors grew larger. This shows that these specific macrophages were preventing the melanoma from growing.

Watching cancer cells being eaten in real time

"Macrophages have always been known as the body's housekeepers – they clear away dead cells and debris," explains Professor Tri Phan, senior author on the paper. "What Dr Keith caught on camera was these cells actively nibbling away and engulfing live cancer cells, constraining tumor growth. Critically, this attack appears to occur independently of T cells and B cells – the immune players most commonly credited with fighting cancer – which made the discovery unexpected, and genuinely exciting."

Implications for immunotherapy

The team's next step is to understand exactly how these CD169-positive macrophages communicate with T cells.

"If we can harness this population of macrophages, we potentially have an immune army already in place, ready to be mobilised," says Professor Phan. "Future treatments could involve developing targeted drugs that boost their numbers, or make them 'hungrier' or better at tagging cancer cells for killing. By combining this approach with existing therapies, we could potentially make immunotherapy work for a much larger group of patients. This could also apply to many cancers beyond melanoma, as macrophages are highly abundant in most solid tumors."

Source:

Garvan Institute of Medical Research

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